(a) Field of the Invention
The present invention relates to a controlled-release composition and a controlled-release microsphere containing an exendin as an active ingredient, and a method of preparing the same.
(b) Description of the Related Art
Exendins are glucagon-like peptide 1 (GLP-1) agonists acting as a GLP-1 hormone in the body, and exendin-4 has 53% sequence homology with the amino acid sequence of GLP-1(7-36)NH2 (Goke, et al., J. Biol. Chem., 268: 19650-19655, 1993).
GLP-1, a representative incretin hormone, is a peptide secreted from L cells in the intestine, is secreted when food inflow into the digestive track occurs, and lowers the blood-sugar level by stimulating insulin secretion from pancreatic beta-cells (Orskov, et al., Diabetes, 42:658-661, 1993). Further, GLP-1 inhibits glucagon release from pancreatic alpha-cells (D′Alessio, et al., J. Clin. Invest., 97:133-138, 1996), and increases gastric-intestinal emptying time resulting in inhibition of food intake (Schira, et al., J. Clin. Invest., 97:92-103, 1996). GLP-1 has functions not only to stimulate insulin secretion from pancreatic beta-cells, but also to increase proliferation rate and survival rate of beta cells (Buteau, et al., Diabetologia, 42:856-864, 1999). However, GLP-1 loses its function by cleavage of its N-terminal region by dipeptidyl peptidase-4 (DPP-4), and has a very short half-life of about 2 minutes (Pridal, et al., Eur. J. Drug. Metab. Pharmacokinet., 21:51-59, 1996; Deacon, et al., Diabetes, 47:764-769, 1998).
Exendins have been known to increase insulin secretion depending on the blood-sugar level in the body, to inhibit postprandial glucagon release, and to lower gastric-intestinal emptying rate resulting in inhibition of food intake. In addition, exendins have an advantage of having a longer half-time than GLP-1, since exendin, unlike GLP-1, is not cleaved at the N-terminal region by DPP-4, and thus exendins can exhibit its function in the body for a longer time than GLP-1 (Thum, et al., Exp. Clin. Endocrinol. Diabetes., 110:113-118, 2002). Exendins are found in salivary secretions of the Gila monster and the Mexican Beaded Lizard, wherein exendin-3 is found in a Mexican Beaded Lizard, Heloderma horridum, and exendin-4 is found in a Gila monster, Heloderma suspectum (Eng, J., et al., J. Biol. Chem., 265:20259-62, 1990; Eng., J., et al., J. Biol. Chem., 267:7402-05, 1992).
It has been confirmed by intraperitoneal injections of exendin-4 into diabetic ob/ob mice once per a day that exendin-4 has a prolonged effect of lowering the blood-sugar level (Greig et al., Diabetologia 42:45-50, 1999). Recently, exendin-4 has been formulated as an injection agent that is subcutaneously injected twice daily at a dose of 5 μg or 10 μg. Although exendin is stable against the DPP-4 enzyme, it has been known to cause side effects such as vomiting, nausea, headaches, and the like, when it is subcutaneously injected to a human at a dose of 0.2 μg/kg or more (Drug Development Research, 53:260-267, 2001). For administration of exendins, the dose limit due to the side effects by initial burst and initial high blood concentration is the biggest obstacle to development of a controlled-release agent of exendin.
Generally, a controlled-release agent of an aqueous drug exhibits a very high release at the initial stage after administration, and there have been various studies to decrease the excessive initial burst. In particular, in developing a controlled-release agent of exendins, decreasing the initial burst is indispensable for preventing side effects such as vomiting, nausea, headaches, and the like caused by the excessive initial burst.
In order to decrease the initial burst of controlled-release microspheres containing octreotide having a therapeutic effect on acromegaly and the like, there has been a study to prepare microspheres by preparing a primary emulsion of the drug together with glucose, and then performing a double emulsion method. In this study, it has been revealed that the initial burst can be decreased by loading the drug together with glucose. However, under a preparation condition in which the initial burst from microspheres is about 5%, the addition of glucose cannot lead to an increase in loading amount, and rather increases the initial burst (J. Wang et al., Biomaterials, 25:1919-1927, 2004).
Therefore, the technique disclosed in the above document is difficult to apply to preparation of a controlled-release formulation of an exendin wherein the initial burst should be 5% or below to decrease side effects caused by the initial burst.
U.S. Pat. No. 7,164,005 and US2005/0271702 disclose a method of preparing exendin-containing microspheres by a phase-separation method using a poly(lactide-co-glycolide) (PLGA) polymer where the ratio of lactide:glycolide is 50:50. In the above documents, polymer 3A (IV=0.38 dL/g), polymer 4A (IV=0.42 dL/g), and the like, particularly polymer 4A, provided by Alkermes Inc., are used as the polymer. In the above documents, the microspheres are prepared by mixing a peptide drug with salting-out components such as ammonium sulfate and sugars such as sucrose and mannitol to prepare a primary emulsion, in order to improve the bioavailability of the microspheres consisting of an exendin and polymer 3A, or 4A, and the stability of the peptide drug. That is, the documents intend to improve the bioavailability by adding additives such as sugars, ammonium sulfate, and the like, thereby allowing sufficient release of an exendin from the polymer matrix. As a result, the bioavailability can be improved to some degree, but the Cmax value is also high, thereby generating the problem of side effects caused by a high initial burst. That is, when the bioavailability becomes high, the initial burst becomes excessive, while when the initial burst becomes low, the bioavailability becomes low.
As described above, the existing techniques of preparing a controlled release microsphere have limitations in that the prepared microsphere has an excessively high initial burst and insufficient bioavailability to be applied to preparation of exendin-containing controlled-release microspheres that require minimization of side effects caused by high initial burst together with improved bioavailability.
Therefore, to solve the above problems, it is necessary to develop a biodegradable exendin-containing formulation exhibiting a low initial burst and improved bioavailability.